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- Berbyuk, Viktor, 1953
(författare)
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Inverse dynamics and Fourier-based approach to solve optimal control problems for multi-link mechanisms
- 1997
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Ingår i: The NATO Advanced Study Institute on Computational Methods in Mechanisms. ; 2, s. 431-440
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Konferensbidrag (refereegranskat)abstract
- This paper is concerned with the investigation of multi-link mechanism controlled motion between fixed boundary conditions and given constraints on the phase coordinates. The moduli of the controlling moments at the hinges between the links are bounded. A computational method to the mathematical modeling of the optimal control laws which govern multi-link mechanism reaching motion is presented. This method is based on Fourier and spline approximations of the independently variable functions and inverse-dynamics approach. The method proposed makes it possible to satisfy the boundary conditions and some constraints on the phase coordinates automatically and accurately. The efficiency of the proposed method is illustrated by the solution of the energy-optimal control problem of a plane mobile three-link manipulator with a load on the grip.
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| 3. |
- Svoboda, Ales, et al.
(författare)
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Simulation of hot isostatic pressing of a powder metal component with an internal core
- 1997
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - 0045-7825 .- 1879-2138. ; 148:3-4, s. 299-314
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a finite element simulation of the thermomechanical phenomena occurring during Hot Isostatic Pressing (HIP) of a powder metal component which includes a graphite core. The thermomechanical coupling is achieved in a staggered step manner. The staggered step approach considers the coupled thermomechanical response of solids, including nonlinear effects in both the thermal and mechanical analyses. The creep behaviour of the powder material during densification is modelled using the constitutive equations of thermal elasto-viscoplastic type with compressibility. The various mechanical material properties are assumed to be functions of temperature and relative density. The mechanical solution also includes large deformation and strains. The thermal problem includes temperature and relative density dependent specific heat and thermal conductivity. The constitutive equations and relations for thermal characteristics are implemented into the implicit nonlinear finite element code, PALM2D. The simulation of the HIP process of a component with internal core is chosen as an application example. The component, injection molding tool, is produced of a hot isostatically pressed stainless tool steel with an internal cavity which is achieved by inserting a graphite core into the HIP container. To verify the result of the simulation, the geometry of the capsule and the coated core are measured both before and after pressing using a computer controlled measurement machine (CMM). The measured geometry is compared with the simulated final shapes of the container and internal core. A computer-aided concurrent engineering system (CACE) is used for the complete manufacturing process from the design of the component and finite element simulation to the inspection of the final geometry.
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| 4. |
- Berbyuk, Viktor, 1953, et al.
(författare)
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Internal torques of human upper extremity during its optimal motion in vertical plane
- 1997
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Ingår i: The Tenth Biomechanics Seminar. - 1100-2247. ; 10, s. 66-83
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Konferensbidrag (refereegranskat)abstract
- In the paper a number of optimal control problems for the motion of the human upper extremity (HUE), for different types of working tasks, are considered. The performance index used in these problems is the integral over the duration of the working task of the sum of the square of the controlling stimuli acting at the joints of the human arm. Under some conditions this performance index can be used for evaluation of the muscles' energy expenditure during human movements. The HUE is simulated by a plane multibody system of rigid masses. The system comprises the three elements with mass and rotatory inertia modelled the upper arm, the forearm and the hand. The controlled motions of the mechanical system are described in terms of joint angles and Cartesian coordinates of the shoulder joint, through the application of Lagrange's equations. The main aim of the study is an investigation of the interaction between the gravity forces and the internal torques acting at the joints during goal-directed extremal motions of the HUE. The analysis of the internal torques, energetic and viscoelastic characteristics of the shoulder, the elbow and the wrist joints for the exstremal controlled motions of the human arm under the external load acting on the hand has been done.
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| 6. |
- Strömberg, Niclas, 1968-
(författare)
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An augmented Lagrangian method for fretting problems
- 1997
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Ingår i: European journal of mechanics. A, Solids. - : Gauthier-Villars. - 0997-7538 .- 1873-7285. ; 16:4, s. 573-593
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Tidskriftsartikel (refereegranskat)abstract
- The present work concerns the numerical treatment of fretting in the interface between a body and a rigid foundation. Starting from a variational formulation of a fretting model given in a framework of continuum thermodynamics, an augmented Lagrangian formulation is derived by introducing finite element discretizations in space and a finite difference discretization in time. The augmented Lagrangian formulation is implemented and solved by a Newton method for the two-dimensional case.
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| 10. |
- Hultén, Lars A. R., 1964
(författare)
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Container Logistics and its Management
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work research on container logistics and its management is presented. Contrary to the common approach of treating this as a mathematical problem and addressing it by operations research methods, this work regards the problem in a wider perspective. Instead of being limited to management of the physical system bringing about the movement of containers, container logistics management is regarded as also including demand management. The research aims at describing the logistics of the system in terms of how the various components in a container transport system interact and how the system interacts with its environment. Due to the limited previous research on container logistics and its management in a wider perspective, this work is primarily explorative and descriptive. Empirical studies of container flows are presented. Both the flow for an individual carrier and the total flow between a port and its hinterland have been studied and the studies reveal a low utilization of the containers. Containers were found to be stored empty for long periods of time at terminals, retained for a considerable time by customers and there was much transport of empty containers. The studies also revealed poor quality of the data in the computerized tracking systems with missing and erroneous data entries. In a study of ten of the world's twenty largest container shipping companies it was found that the use of advanced decision support systems, taking advantage of operations research or artificial intelligence technology, was scarce. Only one company reported to use such a system, which assigned priorities to depots, in day-to-day operations. The main logistical functions of the container are to create opportunities to exploit economies of scale and enabling vessels and vehicles to operate independently by decoupling them at terminals. Therefore, when deciding on actions to improve the utilization of containers the effect on other system components must be considered. Pooling is suggested as a way of increasing the utilization of the containers without constraining the operation of other, capital intensive, resources. Container logistics systems are characterized by high complexity and uncertainty. Much of the information relevant for decision-making is informal and the managers' experience is difficult to formalize. Therefore successful systems for container logistics management must take advantage of both human and computerized information processing. It is suggested to engage theories from cybernetics and information theory as a theoretical framework for logistics systems analysis. Even if this is only done to a limited extent in this research, due to being considered at a late stage of the research, these theories show a strong explanatory ability.
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